Meter reading methods and apparatus

ABSTRACT

Meters having a plurality of rotating dials are read automatically by using radiant energy to sense the angular positions of the dials. A single radiant energy detector is time-shared among the several dials to reduce the cost of the meter reading apparatus. The meter can transmit meter readings and other information to remote locations. It can also receive, store, and act upon information received from remote locations. The meter can measure short-term demand, and can produce output signals for indicating and/or controlling demand.

BACKGROUND OF THE INVENTION

This invention relates to methods and apparatus for reading meters,particularly those having a plurality of rotating dials. The inventionalso relates to meter reading apparatus for performing relatedcommunications and control functions.

It has long been recognized that automatic reading of meters, such aselectric and gas utility meters, would be highly desirable. One of themajor obstacles to implementing such systems has been the relativelyhigh cost of the meter reading apparatus which must be associated witheach meter. In a typical electric or gas utility system having tens ofthousands or even hundreds of thousands of meters, minimizing individualmeter cost is essential to an economically viable automatic meterreading system. The difficulty of converting to automatic meter readingcapability large numbers of existing meters, of which there may beseveral different types in use in a single utility system, is anotherextremely important consideration. Although several automatic meterreading systems have been proposed, none has been widely adopted, atleast partly because of the relatively high cost or other disadvantagesof the additional apparatus required in association with each meter.Among the other disadvantages of many of the previously proposed systemsis the requirement for battery back-up to retain stored data duringpower outages.

To take full advantage of automatic meter reading, it is desirable forthe meter to be able to transmit its readings to remote locations.Systems with that capability have been proposed, as shown, for example,by Sellari U.S. Pat. No. 3,588,357. However, it would also be desirableto be able to control various functions of the meter from remotelocations for such purposes as meter reading on command, controlingindividual utility customer demand, and/or controlling overall systemdemand.

In view of the foregoing, it is an object of this invention to provideimproved and simplified automatic meter reading methods and apparatus.

Another object of this invention is to provide low cost but highlyreliable automatic meter reading methods and apparatus.

Still another object of this invention is to provide automatic meterreading methods and apparatus which can easily and economically appliedto many different types of existing meters.

Yet another object of this invention is to provide solid stateelectronic meter reading and control apparatus which can recover from apower outage without the aid of battery back-up.

Still another object of this invention is to provide automatic meterreading methods and apparatus including the capability of transmittinginformation to remote locations and receiving information from remotelocations.

Yet another object of this invention is to provide automatic meterreading methods and apparatus including the capability of generatingsignals for at least partially controlling the use of the meteredservice based on service demand as measured by the meter, controlparameters stored in the meter as a result of either local or remotecontrol of the meter, and the like.

SUMMARY OF THE INVENTION

These and other objects of the invention are accomplished in accordancewith the principles of the invention by mounting a patterned disc forrotation with each of the dials of a meter having a plurality of suchdials. Each disc has sectors of different radiant energy attenuatingproperties. Radiant energy is directed to the discs one at a time insuccession so that the radiant energy directed to each disc is encodedby the sectored pattern of that disc. The encoded radiant energy isdirected from each disc to a single sensor location. A sectored detectoris disposed at the sensor location so that each detector sector receivesa portion of the encoded radiant energy and produces an output signalindicative of the intensity of the received encoded radiant energy. Theoutput signals of the sectored detectors are processed to determine theangular position of the disc to which radiant energy is currently beingdirected. The angular positions of all of the dials are determined inthis manner to provide a complete reading of the meter.

The meter may produce output signals for transmitting its readings andother information to a remote location. The meter may also be capable ofreceiving, storing, and acting upon control signals and otherinformation received from a remote location. The meter may also visuallydisplay its readings and other information.

The meter may also include methods and apparatus for automaticallymeasuring the short-term demand for the service or commodity beingmetered. For example, in an electric meter having a rotating eddycurrent disc, the number of rotations of the disc in a predeterminedtime interval (e.g., 1 minute, 15 minutes, 30 minutes, etc.) can bedetermined by counting the number of times during that time intervalthat a non-reflective spot or mark on the disc passes a predeterminedreference point. The meter may transmit its demand readings to a remotelocation in a manner similar to transmission of usage readings.Alternatively or in addition, the meter may process the demand readings,typically in conjunction with demand limits or other information storedin the meter either locally or remotely or both, to produce outputsignals for controlling apparatus which is or may be responsible for thedemand.

Further features of the invention, its nature and various advantageswill be more apparent from the accompanying drawings and the followingdetailed description of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partly sectional plan view of an illustrative electricutility meter modified in accordance with the principles of thisinvention.

FIG. 2 is an elevational view of the meter of FIG. 1 taken along theline 2--2 in FIG. 1.

FIG. 3 is a schematic drawing of a portion of the electronic circuitryfor the meter of FIGS. 1 and 2.

FIGS. 4a-c, which are to be assembled as shown in FIG. 4d, arecollectively a schematic diagram of another portion of the electroniccircuitry for the meter of FIGS. 1 and 2.

FIG. 5 is a detailed elevational view of a portion of the apparatus ofFIGS. 1 and 2.

FIG. 6 is a cross sectional view taken along the line 6--6 in FIG. 5.

FIG. 7 is an elevational view of an illustrative optical assembly foruse in the meter of FIGS. 1 and 2.

FIG. 8 is a cross sectional view taken along the line 8--8 in FIG. 7.

FIG. 9 is an elevational view of the apparatus of FIGS. 7 and 8 taken inthe opposite direction from FIG. 7.

FIG. 10 is a cross sectional view taken along the line 10--10 in FIG. 9.

FIG. 11 is a simplified perspective view of an illustrative opticalsystem for use in the meter of FIGS. 1 and 2.

FIG. 12 is a flow chart of the operation of the microcomputer employedin the electronic circuitry of FIG. 4.

FIGS. 13, 14a-f, 15, and 16a-c are more detailed flow charts of portionsof the FIG. 12 flow chart.

DETAILED DESCRIPTION OF THE INVENTION

Although certain aspects of this invention are applicable to readingmany different types of meters having a plurality of rotating dials,those aspects of the invention will by fully understood from anexplanation of their application to a typical electric utility watthourmeter.

As shown in FIGS. 1 and 2, a typical watthour meter 10 includes aplurality of rotating dials 12a-e for indicating, in any convenientnumber system such as base 10, the amount of electrical energy consumedin the circuit monitored by the meter. In the depicted embodiment thereare five dials 12, the angular position of each of which represents onedigit of a five-digit decimal number. Although the depicted meter hasefive dials 12, it will be understood that the meter could have anynumber of such dials.

Affixed to each dial 12 is a patterned disc 20 of the type shown anddescribed in commonly assigned Burrowes et al. U.S. patent applicationSer. No. 624,156, filed June 25, 1984 now U.S. Pat. No. 4,587,513(hereinafter "Burrowes et al."), which is hereby incorporated byreference herein. Although one particular disc configuration is employedin the depicted embodiment, it will be understood that any of the discconfigurations taught by Burrowes et al. could be used. In the depictedembodiment each disc 20 is a circular and is mounted on the associateddial 12 for concentric rotation therewith as shown in detail in FIGS. 5and 6. Each disc is preferably shaped to conform to the associated dialso that the disc can be simply pressed on over the dial. If desired, anysuitable means, such as an adhesive, can be used for securing discs 20to dial 12. The exposed face of each disc 20 has two bilaterallysymmetrical sectors 22 and 24. Sectors 22 and 24 have substantiallydifferent radiant energy attenuating characteristics. For example,sector 22 may reflect substantially more radiant energy than sector 24if, as in the depicted embodiment, reflected radiant energy is employedto read meter 10.

A plurality of radiant energy sources 30a-e (only one of which isvisible in FIG. 2) is mounted in front of discs 20a-e so that radiantenergy from each source 30 is directed to a respective one of discs 20(see also FIG. 11). In the particular embodiment shown in the drawings,sources 30 are infrared light emitting diodes ("LEDs"). Sources 30 areenergized one after another in a predetermined sequence by electricalcontrol circuitry described in detail below. Because of the differingradiant energy attenuating properties of the two sectors 22 and 24 ofeach disc 20, the radiant energy reflected by each disc encodes theangular position of the disc as taught by Burrowes et al.

Radiant energy reflected by each disc 20 is directed to a single sensorlocation 50 by a plurality of lenses 40a-e, each of which is disposedalong an axis between a respective one of disc 20a-e and sensor location50 (See FIG. 11). Each lens 40 is shaped to focus the radiant energyreflected by the associated disc at sensor location 50. A particularlypreferred lens assembly is shown in detail in FIGS. 7-10 and describedbelow.

Sectored detector 60 is disposed at sensor location 50 to receive thereflected radiant energy from each of lenses 40. Detector 60 may besimilar to the detectors shown by Burrowes et al. Accordingly, detector60 is divided into four equal, angularly distributed quadrants, each ofwhich receives a sector of the encoded radiant energy from the disc 20which is currently exposed to radiant energy from one of sources 30.Each sector of detector 60 produces an electrical output signalproportional to the amount of radiant energy received by that detectorsector. The four output signal of detector 60 are analyzed in the mannertaught by Burrowes et al. to produce data words indicative of theangular position of the disc 20 currently supplying encoded radiantenergy to detector 60. This corresponds to the angular position of themeter dial 12 associated with that disc. This partial meter readinginformation is combined with similar information for each dial 12 toproduce a complete reading of the meter.

It should be noted that everything which must be added to theconventional meter apparatus in accordance with this aspect of theinvention can typically be added in front of dials 12. This is true ofdiscs 20, sources 30, lenses 40, and detector 60. It is also true of (1)circuit board 100 which carries substantially all of the electroniccircuitry needed to control the foregoing meter reading operation andother related functions described in detail below, and (2) heat sink andcover plate assembly 102 which is mounted over circuit board 100. Thearrangement of the apparatus of this invention greatly facilitatesmounting of the apparatus on a wide variety of conventional meters. Theassociated meter apparatus can be basically unchanged. Accordingly, theapparatus of this invention can be easily and inexpensively added tomany different types of known meters.

For monitoring short-term power demand, a reflective sensor assembly 80is mounted adjacent to one planar surface of the rotating eddy currentdisc 16 in meter 10 so that radiant energy produced by sensor assembly80 is reflected back to that assembly from the surface of disc 16. Thetypical eddy current disc 16 is made of a highly reflective metal. Oneor more small, radial, partially reflective marks (not shown) are addedto the surface of disc 16 which is exposed to radiant energy from sensorassembly 80. Accordingly, the amount of reflected radiant energyreceived by sensor assembly 80 is used to detect the passage of thepartially reflective mark or marks on disk 16. Short-term demand iscalculated by counting the number of times a partially reflective markpasses sensor assembly 80 in a predetermined period of time (e.g., 1,15, 20, 30, 40, or 60 minutes) and scaling that number in accordancewith the predetermined calibration factor of the meter.

FIGS. 3 and 4 depict illustrative electronic circuitry, located for themost part on circuit board 100, for use as part of the automatic meterreading apparatus of this invention. FIG. 3 is an illustrative powersupply circuit, and FIGS. 4a-c (which go together as shown in FIG. 4d)are the main logic and control circuit.

As shown in FIG. 3, connector jack J1 is connected to the power circuitbeing metered, typically a 220 volt, two phase, alternating current("AC") power circuit. This connection is preferably made upstream of anypower circuit control device controlled by the apparatus of thisinvention as discussed in detail below so that the circuitry of thisinvention is powered even if power has been cut off to the customerbeyond the meter. The power supply circuit is protected by fuse F1.Transformer T1 applies 12 volt alternating current electrical power toterminals D and E of connector P1. Relatively high frequency (e.g., 125KHz) data signals are superimposed on both phases of the power signalcircuit by way of connector P1 terminals 1 and A and low frequencyblocking capacitors C1 and C2. Communication via these high frequencydata signals (also known as power line carrier or PLC signals isbidirectional. Accordingly, PLC signals can pass either (1) from thepower signal circuit (either or both phases) connected to jack J1 toconnector P1 terminals 1 and A, or (2) from terminals 1 and A to thepower signal circuit (both phases). PLC signals received via one powersignal phase are coupled to the other power signal via the lower coil oftransformer T2 (FIG. 4a). In addition, the apparatus of this inventioncan be used to receive PLC signals from either power signal phase andthen retransmit those signals via both phases as described in detailbelow. Conventional metal oxide varistor MOV provides overvoltage(surge) protection.

Connector P1 terminals D, E, 1, and A are respectively connected toterminals D, E, 1, and A of connector J1 in FIG. 4a. The 12 volt ACsignal from terminals D and E is applied to conventional bridgerectifier BR1 and then to conventional voltage regulator IC-6. (All ofthe IC parts shown in FIG. 4 can be commercially available devices. Alist of suitable devices will be found below following the discussion ofFIG. 4.) The +5 volt output signal of IC-6 (applied to common point A)is used throughout the FIG. 4 circuitry as a logic and power signal. Forexample, the VCC input terminal of microcomputer IC-7 (described indetail below) is connected to +5 volt common point A. The +5 volt signalat common point B and the +15 volt signal at common point C are similar.In the event of a power failure, the energy stored in capacitor C14allows the FIG. 4 circuitry to continue to function long enough (e.g.,approximately 20 milliseconds) to store the time of the failure in anelectrically erasable programmable read-only memory ("EEPROM") IC-8 andto complete any other IC-8 erase/write cycle then in progress.

The 12 volt AC signal applied to connector J1 terminal D is alsoapplied, via resistor R15 and transistor Q2, to the P3,4 input terminalof microcomputer IC-7 (FIG. 4b). Microcomputer IC-7 may be any suitablemicrocomputer such as an 8751H-8 EPROM microcomputer available fromIntel Corporation of Santa Clara, Calif. This device includes amicroprocessor, an on-board memory, and input/output ports. The ACsignal applied to IC-7 terminal P3,4 is used to control a real-timeclock function performed by IC-7.

The +5 volt output signal of IC-6 is applied to conventional resetdevice IC-5. IC-5 monitors the output signal of IC-6 to detect a powerfailure and to reset IC-7 via the RST terminal of IC-7 after power hasbeen restored. The RS BAR output signal of IC-5 is applied to IC-3 andIC-7 to prevent any PLC signal transmission during a reset operation.

IC-3 is a conventional communications circuit for modulating anddemodulating PLC signals. PLC signals received via connector J1terminals 1 and A are amplified and applied to IC-3 via elements T2,R12, and Q1. Received PLC signals are demodulated by IC-3 and applied toterminal P3,0 of IC-7. These received PLC signals typically representcommands and/or data for controlling the operation of meter 10 asdiscussed in detail below. The ultimate source of these commands and/ordata is typically a central facility of the utility company. Data to betransmitted via PLC signals is generated by IC-7 and applied to the TXterminal of IC-3. IC-3 uses this data to modulate a carrier signalapplied to the I/O terminal of IC-3. The resulting PLC output signal isapplied to J1 connector terminals 1 and A via resistor R12 andtransformer T2 for transmission to a remote location. The remotelocation may be (1) one or more control elements on the premises servedby meter 10, (2) a central facility of the utility company, or (3) othersimilar remote apparatus. Illustrative PLC signals transmitted by meter10 include the above-described automatic meter readings.

The radiant energy sources 30a-e of Figures 1 and 2 are shownschematically in FIG. 4a as fmeter readings.

The radiant energy sources 30a-e of FIGS. 1 and 2 are shownschematically in FIG. 4a as five infrared light emitting diodes ("LEDs")D1-D5. Illumination of D1-D5 is controlled by IC-7. The P0,2 throughP0,7 output signals of IC-7 are applied to IC-1 in parallel withconventional pull-up resistor network RN1. IC-1 is a conventionalbuffer. The P0,2 through P0,6 signals control illumination of D1-D5,while the P0,7 signal controls illumination of the LED in the REFLECTIVESENSOR element also shown in FIG. 4a and discussed in detail below. Themanner and sequence in which these devices are illuminated is discussedin detail below in relation to FIGS. 12-16. The output signals on IC-1pins 11-15 are respectively applied to the cathodes of D3, D4, D5, D2,and D1 via connectors J2 and P2. The anodes of D1-D5 are connected incommon to elements R1-R4 and IC-2 which collectively control thebrightness of D1-D5 and the LED in the REFLECTIVE SENSOR under thecontrol of the P2,3-P2,6 output signals of IC-7. IC-2 is a conventionaleight-channel sourcing (open collector) buffer.

The sectored detector 60 of FIGS. 1 and 2 is shown in FIG. 4c as theQUAD SENSOR device. The four sectors of detector 60 are respectivelyrepresented by photo-sensitive diodes A-D in the QUAD SENSOR device.These four sectors are sampled one at a time in succession byconventional multiplexer device IC-12 under the control of the P2,0 andP2,1 output signals of IC-7. The sampling rate of diodes A-D issynchronized with the energization of LEDs D1-D5 so that the QUAD SENSORsectors are sampled during multiple successive energizations of eachLED. The manner and sequence in which the QUAD SENSOR sectors aresampled is discussed in more detail below in relation to FIGS. 12-16.The output signal of the QUAD SENSOR sector currently being sampled ispre-amplified by IC-11 operational amplifier 8-9-10. The rapidlytime-varying component of the pre amplified by IC-11 operationalamplifier 12-13-14. The output signal of post-amplifier 12-13-14 isapplied to the CH8 input terminal of conventional multi-channelanalog-to-digital (A/D) converter IC-10. When enabled by suitable chipand channel select signals from IC-7, IC-10 converts the analog signalapplied to input terminal CH8 to a serial digital output signal appliedto IC-7. IC-11 amplifier 1-2-3 supplies a +3 volt reference signalrequired by IC-10. Based on successive digital input signalsrepresenting the output signals of the four QUAD SENSOR sectors, IC-7computes the angular position of the meter dial 12 associated with eachdisc 20. The angular position determining algorithm can be similar tothat disclosed by Borrowes et al.

As mentioned above, the meter reading thus determined by IC-7 can betransmitted to another location by the above-described PLC signals. IC-7applies a serial digital data signal representative of the meter readingto its P3,1 output terminal. IC-3 uses this digital data signal tomodulate the PLC carrier signal applied to both phases of the 220 voltAC power signal circuit via transformer T2 and the power supply circuitof FIG. 3.

In addition to transmitting meter readings to remote locations via PLCsignals, IC-7 transmits the meter reading information to conventionaldisplay driver IC-9 for use in controlling a conventional seven-segmnetplus decimal point DISPLAY device which is preferably visible to anyoneobserving the meter. The DISPLAY device successively displays decimaldigits indicative of the complete meter reading, each decimal digitrepresenting the angular position of a respective one of meter dials 12.The decimal digits are displayed in decimal order (most significantlyfirst), and all segments of the DISPLAY (including the decimal point("DP")) are illuminated after the least significant digit of each meterreading as DISPLAY test and framing information to enable the reader ofthe DISPLAY to determine the significance of the digits displayed.

The meter of this invention is also capable of reading the short-termpower demand in the power circuit to which the meter is connected. Thisis accomplished by the REFLECTIVE SENSOR device shown in FIG. 4a, whichcorresponds to reflective sensor assembly 80 in FIGS. 1 and 2. TheREFLECTIVE SENSOR includes a light emitting diode ("LED") for directingradiant energy to the surface of eddy current disc 16. Radiant energyreflected from the eddy current disc is detected by the photo-sensitivediode which is the other REFLECTIVE SENSOR component. Accordingly, theREFLECTIVE SENSOR can be used to detect the passage of theabove-mentioned partially reflective mark or marks on the eddy currentdisc 16. The output signal of the REFLECTIVE SENSOR photodiode diode isamplified by IC-11 operational amplifier 5-6-7 for application to CH4 ofIC-10. As in the case of the QUAD SENSOR output signals, IC-10 digitizessuccessive samples of the CH4 analog input signal and applies theresulting digital data signals to IC-7. IC-7 determines from thesesignals the number of times that the non-reflective mark on eddy currentdisc 16 passes the REFLECTIVE SENSOR in a predetermined time interval(e.g., 1 minute, 15 minutes, 30 minutes, etc.). On that basis, IC-7computes the short-term power demand in the power circuit monitored bymeter 10.

The above-described power demand determination can be used in severalways. For example, it is customary to place customers who are delinquentin paying for the electricity they have used on limited service in whichthe customer's demand is not to exceed a predetermined relatively smallmaximum (so-called LIFE LINE service). If the customer served by meter10 is on LIFE LINE service, the permissible maximum demand value istransmitted to meter 10 via the above-described PLC signals and storedin IC-7. Thereafter, IC-7 continually compares the actual demand to thepredetermined maximum, and if the maximum is exceeded, IC-7 producesP2,7 output signals applied to connector J1 LIFE LINE terminal 5 viaIC-2 and IC-1 for controlling a conventional switching device (notshown) which cuts off all power to the customer. (LIFE LINE terminal 5is normally high, and is pulled low by the above-described P2,7 outputsignal in order to trigger the LIFE LINE switching device.)

Another potential use of the above-described demand determination is tocut off certain customer apparatus in the event that the customer'sdemand exceeds a predetermined threshold value stored in IC-7. Thisfeature can be used by the utility company to help reduce overall systemdemand peaks and to smooth out demand over time. The threshold value istransmitted to meter 10 via the above-described PLC signals and storedin IC-7. IC-7 compares the threshold value. If actual demand exceeds thethreshold, IC-7 produces a P0,0 or P0,1 output signal which is applied,via conventional optical isolator IC-4, to connector J1 DEMAND CONTROLterminals C and 3 (FIG. 4a). These DEMAND CONTROL terminals areconnected to a relay-type device (not shown) which cuts off power to oneor more of the customer's electrical appliances, e.g., a hot waterheater. Alternatively or in addition, control signals for shutting offpower to selected devices can be applied by IC-7 to the above-describedPLC channel. The actual demand data can also be applied to the PLCchannel by IC-7.

The FIG. 4 circuitry also includes a thermistor THM (FIG. 4c) formonitoring the temperature in meter 10. Excessive meter temperature mayindicate impending failure of the meter. A sudden change in metertemperature may indicate tampering with the meter. The analog outputsignal of thermistor THM is applied to IC-10 input terminal CH5 andconverted to digital signals applied to IC-7 in the same manner as theQUAD SENSOR analog output signal is digitized and applied to IC-7. Ifthe thermistor output signal changes rapidly or exceeds a predeterminedthreshold value, IC-7 sends out appropriate warning signals via theabove-described PLC channel.

The following is a list of commercially available devices which can beused for the principal components shown in FIG. 4:

    ______________________________________                                        Reference                 Manufacturer's                                      Number   Manufacturer     Designation                                         ______________________________________                                        IC-1     Sprague          ULN-2003A                                           IC-2     Sprague          UDN-2585A                                           IC-3     National Semiconductor                                                                         LM1893N                                             IC-4     Litronix         4N36                                                IC-5     Texas Instruments                                                                              TL7705A                                             IC-6     Texas Instruments                                                                              7805CKC                                                                       (78M05CKC)                                          IC-7     Intel            8751H-8                                                                       EPROM                                                                         MICROCOMPUTER                                       IC-8     National Semiconductor                                                                         NMC494                                                                        EEPROM                                                                        16 × 16 BIT                                   IC-9     Sprague          UDN-2585A                                           IC-10    National Semiconductor                                                                         ADC0811CN                                                                     11CH 8 BIT                                                                    A/D W/HOLD                                          IC-11    Texas Instruments                                                                              TLC27M4CN                                                                     CMOS QUAD                                                                     OP-AMP                                              IC-12    RCA              CD4051BE                                                                      CMOS 8CH                                                                      ANALOG MUX                                          ______________________________________                                    

FIG. 12 shows the overall operating sequence 200 that IC-7 is programmedto perform. When the apparatus is started for the first time, or afterany power outage, trap timeout, or power fault, processing begins withthe resetting of IC-7 at step 202. (A trap timeout will occur if theIC-7 program becomes stalled for a period of time in excess of apredetermined trap timeout interval.) At step 210 IC-7 performs variousinitializaiton tasks including initializing its input and output ports,initializing its interrupts and timers. initializing its communicationscontrol information, and initializing various variables used throughoutthe program. Initialization routine 210 is shown in greater detail inFIG. 13. At step 230 IC-7 performs its main program loop which includessuch tasks as waiting until data (e.g., QUAD SENSOR data) has beenacquired, adjusting the drive current for LEDs 30, calculating thepositions of meter dials 12, updating the stored data base, andcontrolling the LIFELINE and DEMAND CONTROL functions. Main program 230is shown in greater detail in FIG. 16.

Main program 230 (or communications interrupt routine 400) isinterrupted every 1.04166 . . . milliseconds by timer interrupt routine280. This timer interrupt routine frequency synchronizes the 64 samplesof each QUAD SENSOR sector (described below) with the 60 Hz power signalcycles in order to substantially cancel out the effects of any 60 Hznoise. (Each 60 Hz power signal cycle takes 16.6666 . . . milliseconds.16.6666 . . . divided by 16 equals 1.04166 . . . .) Timer interruptroutine 280 (shown in greater detail in FIG. 14) performs such functionsas dial reading data acquisition, keeping time, counting eddy currentdisc revolutions as a basis for short-term demand determinations,performing EEPROM operations, and performing display functions utilizingthe FIG. 4b DISPLAY.

Communications interrupt routine 400 (shown in greater detail in FIG.15) interrupts main program 230 (but not timer interrupt routine 280)whenever IC-3 signals that a byte of PLC data has been received ortransmitted. Communications interrupt routine 400 performs suchfunctions as limiting external PLC access to preclude tampering via thePLC channel with such data as the meter serial number and calibrationfactor, facilitating the reading and writing of data control parameters,and periodically outputting PLC data to be transmitted.

As mentioned above, initialization routine 210 is shown in more detailin FIG. 13. At step 212 the initialization operations mentioned above inconnection with FIG. 12 are performed. At step 214 nonvolatile EEPROMmemory IC-8 is read to retrieve such information as the identificationnumber of the meter, the calibration factor of the meter, the timeinterval on which short-term demand determinations are to be based, thelifeline service limit, and the status of the meter. At step 216 controlpasses to main program 230.

Timer interrupt routine 280 is shown in greater detail in FIG. 14. Thetimer interrupt routine begins by storing (at step 282) the status ofthe interrupted routine (i.e., either main program 230 or communicationsinterrupt routine 400). At step 284 a steering variable known asINTERRUPT COUNTER is tested, and if it is zero, control passes to step286. Otherwise, control passes to step 292. At step 286 EE FLAG andUPDATE DIAL FLAG variables are tested. The EE FLAG variale is set duringan EEPROM erase/write cycle. In order to conserve power during such acycle, the reading of dials 12 is suspended, although the counting ofeddy current disc revolutions continues. This ensures completion of anEEPROM erase/write cycle even if a power outage has occurred. The UPDATEDIAL FLAG variable is set after sufficient data has been gathered toallow computation of the angular positions of dials 12. While the UPDATEDIAL FLAG is set, no further dial reading data is gathered. If at step286 neither the EE FLAG nor the UPDATE DIAL FLAG variable is found to beset, control passes to step 288. Otherwise control passes to step 314.

At step 288 the brightness control data for the LED associated with thedial 12 to be read is applied to IC-2. Then the appropriate LED isactivated via IC-1. After a time delay, one QUAD SENSOR sector orquadrant is sampled (a so-called "light" sample) and the resulting datais added to the buffer which accumulates data for that QUAD SENSORsector. Lastly, the SAMPLE COUNTER variable is incremented and controlpasses to step 290 in which the termperature of the meter is read usingthermistor THM. Control then passes to step 314.

If at step 284, the INTERRUPT COUNTER variable was found to be otherthan zero, control passes to step 292 where the INTERRUPT COUNTERvariable is tested again. If found to be one, control passes to step 294where the EE FLAG and UPDTE DIAL FLAG variables are tested. Otherwise,control passes to step 300. If at step 294 neither the EE FLAG nor theUPDATE DIAL FLAG variable is found to be set, control passes to step296. Otherwise, control passes to step 314.

At step 296 all of LEDs 30 are turned off. Then there is a time delay,after which one QUAD SENSOR sector or quadrant is sampled (a so-called"dark" sample) and the resulting data is subtracted from the bufferwhich accumulates data for that QUAD SENSOR sector. Thereafter, theSAMPLE COUNTER variable is incremented and control passes to step 298where the power supply voltage level is read to ensure that an EEPROMerase/write cycle is not allowed to begin unless there is sufficientenergy stored in capacitor C14 to complete that cycle. Control thenpasses to step 314.

If at step 292 the INTERRUPT COUNTER variable was found to be other thanone, control passes to step 300 where the INTERRUPT COUNTER variable istested again. If found to be two, control passes to step 302. Otherwise,control passes to step 312.

At step 302 the REFLECTIVE SENSOR associated with eddy current disc 16is read with the REFLECTIVE SENSOR LED off to produce a so-called "dark"sample, and that sample is subtracted from the buffer which accumulatesdata for the eddy current disc. At step 304 the power supply voltagelevel is read as at step 298. At step 306 the brightness control datafor the REFLECTIVE SENSOR LED is applied to IC-2, the REFLECTIVE SENSORLED is illuminated via IC-1, and the eddy current DISC READ COUNTERvariable is incremented. At step 308 the modulo 64 SAMPLE COUNTERvariable is tested and if it is zero. multiplexer IC-12 is reset tocollect data from the next QUAD SENSOR sector or quadrant to be sampled.Control then passes to step 314. If the SAMPLE COUNTER variable is notzero at step 308, control passes directly to step 314. Accordingly, 64alternating "light" and "dark" samples are taken of each QUAD SENSORsector in order to determine the position of each dial 12.

If at step 300 the INTERRUPT COUNTER variable was found to be other thantwo, then control passes to step 312 where the INTERRUPT COUNTERvariable is set to minus 1. Also at step 312 the REFLECTIVE SENSOR LEDis sampled (with the associated LED on as described above in connectionwith step 306) and the resulting "light" sample is added to the bufferwhich accumulates data for eddy current disc 16. Thereafter, allillumination LEDs are turned off via IC-1, the DISC READ COUNTERvariable is incremented, and the temperature of the meter is read viathermistor THM. At step 314 the INTERRUPT COUNTER variable isincremented, At step 316 data is sent to display driver IC-9 to causethe DISPLAY device to display either a decimal point with an 8 (as aDISPLAY test pattern and framing indication) or a decimal digitindicative of the angular position or a desired one of dials 12.Thereafter, a desired one of the EEPROM operations listed in FIG. 14d isperformed. The READ operation allows data to be read from any desiredEEPROM location. The ENABLE ERASE/WRITE operation takes the EEPROM outof its normal DISABLE ERASE/WRITE condition (which protects the EEPROMfrom transients during abnormal conditions such as a power failure). TheSTART ERASE/WRITE operation initiates an erase/write cycle to allow datain the EEPROM to be altered. An erase/write cycle is allowed to beginonly if there is sufficient energy stored in capacitor C14 to completeit. After performing the desired EEPROM operation, control passes tostep 320.

At step 320 the SAMPLE COUNTER variable is tested, and if it is greaterthan 63, control passes to step 322. Otherwise, control passes to step330. At step 322 the SAMPLE COUNTER variable is set to zero and theQUADRANT variable is incremented. At step 324 the QUADRANT variable istested, and if it is greater than 3, control passes to step 326.Otherwise, control passes to step 330. At step 326 the QUADRANT variableis set to zero and the DIAL UPDATE FLAG is set. Control then passes tostep 330.

At step 330 if the DISC READ COUNTER variable is greater than seven,control passes to step 332. Otherwise, control passes to step 350. Atstep 332 the contents of the eddy current disc buffer are divided byfour to compute an AVERAGE and the DISC READ COUNTER variable is resetto zero. Accordingly, the AVERAGE is the average of the differencebetween four "light" and four "dark" samples of eddy current disc 16. Atstep 334, if the AVERAGE value determined in step 332 indicates that theREFLECTIVE SENSOR is saturated, then control passes to step 336 wherethe data controlling the brightness of the REFLECTIVE SENSOR LED isimmediately lowered. Control then passes to step 350. Similarly, at step334, if the AVERAGE indicates that the REFLECTIVE SENSOR is at too low alevel for an extended period (e.g., 20 minutes), then at step 336 thedata controlling the brighness of the REFLECTIVE SENSOR LED is increasedand control passes to step 350. This latter type of adjustment is madeonly after a time delay so that if eddy current disc 16 is moving veryslowly, the prolonged exposure of the REFLECTIVE SENSOR to anon-reflective mark on the disc will not result in a gain adjustment.

If step 334 does not indicate any requirement for adjustment of LEDbrightness, then control passes to step 338 where the AVERAGE from step332 is compared to an upper threshold value of 75. If the AVERAGE isgreater than 75 (indicating that the REFLECTIVE SENSOR is not adjacent anon-reflective mark on eddy current disc 16) and the DISC COUNTERvariable is odd (indicating that a non-reflective mark was adjacent theREFLECTIVE SENSOR the last time the DISC COUNTER variable wasincremented), then the DISC COUNTER is incremented at step 340 to recordthe transition from a non-reflective area to a reflective area on theeddy current disc. Thereafter, control passes to step 350. If step 338produces a negative result, then control passes to step 342. At step 342the AVERAGE from step 332 is compared to a lower threshold value of 65.If the AVERAGE is less than 65 (indicating that the REFLECTIVE SENSOR isadjacent a non-reflective mark on eddy current disc 16) and the DISCCOUNTER variable is even (indicating that no non-reflective mark wasadjacent the REFLECTIVE SENSOR the last time the DISC COUNTER variablewas incremented), then the DISC COUNTER variable is incremented at step340 to record the transition from a reflective area to a non-reflectivearea on the eddy current disc. Thereafter, control passes to step 350.If step 342 produces a negative result, control passes directly to step350.

Step 350 begins the processing of the 60Hz power signal to control thereal time clock variables stored in IC-7. At step 350 the 60 Hz inputport P3,4 is tested. If it is low, the HI FLAG variable is reset at step352. Otherwise, the LOW FLAG variable is reset at step 354. From thestep 352 control passes to step 356 where the LOW FLAG variable istested. If the LOW FLAG is not set, then it is set at step 358 andcontrol passes to step 398 where timer interrupt routine 280 ends byrestoring the status of the program interrupted at the start of thetimer interupt routine and by returning to that program. If at step 356the LOW FLAG variable is found to be set, control passes to step 360where the CNT60 variable is tested. If CNT60 is odd, control passes tostep 398 described above. If CNT60 is even, control passes to step 370where CNT60 is incremented.

Returning to step 354, after that step, the HI FLAG variable is testedat step 362. If found to be reset, HI FLAG is set at step 364, afterwhich control passes to step 398 described above. If at step 362, HIFLAG is found to be set, control passes to step 366 where CNT60 istested. If CNT60 is even, control passes to step 398 described above.Otherwise, control passes to step 370 where CNT60 is incremented asdescribed above.

After step 370, CNT60 is tested at step 372. If CNT60 is greater than7200 (the number of 60 Hz zero axis crossings in one minute), controlpasses to step 374. Otherwise control passes to step 398 describedabove.

At step 374 CNT60 is reset to one, the MINUTE and HR24 variables areincremented, and the NEW MINUTE FLAG is set. At step 376 the MINUTEvariable is compared to the DEMAND PERIOD variable, which is thepredetermined number of minutes (usually 15, 20, 30, 40, or 60) on whichshort-term demand determinations for billing purposes are made. If theMINUTE variable is less than or equal to the DEMAND PERIOD variable,control passes to step 380. On the other hand, if the MINUTE variable isgreater than the DEMAND PERIOD variable, then at step 378 the MINUTEvariable is reset to one and the PERIOD FLAG is set to indicate that ashort-term demand determination should be made. Control then passes tostep 380.

At step 380 the HR24 variable is compared to 1440 (the number of minutesin a 24 hour day). If HR24 is less than or equal to 1440, control passesto step 398 described above. Otherwise control passes to step 382 wherethe HR24 variable is reset to 1 and the DAY28 variable is incremented.At step 384 the DAY28 variable is compared to 27. If DAY28 is less thanor equal to 27, control passes to step 398 described above. If DAY28 isgreater than 27, control passes to step 386 where the PK2 (PEAK2) andDAY28 variables are set to zero. PK2 and PK1 (discussed below) are twosimilar variables related to the customer's peak short-term demand andon which the customer's bill for service may be based in part. PK1 canbe cleared or reset periodically via the PLC channel. PK2 can only bealtered by physical access to the circuitry of the meter. It is resetinternally every 28 days based on the above-described DAY 28 variable.Periodic comparison of PK1 and PK2 can be used to detect unauthorizedtampering with PK1.

Communications interrupt routine 400 is shown in greater detail in FIG.15. As indicated at step 402, main program 230 (but not timer interruptroutine 280) is interrupted by communications interrupt routine 400whenever IC-3 indicates either that a byte of transmitted data has beenreceived or that it has finished transmitting a byte of data. The statusof main program 230 is saved so that processing of the main program canbe resumed when processing of the communications interrupt routine iscomplete. At step 404 it is determined whether the communicationsinterrupt routine was initiated by completion of a data transmission(control passes to step 406) or completion of a data reception (controlpasses to step 410). At step 406 it is determined whether or not all ofthe data to be transmitted has been transmitted. If so, control passesto step 412. Otherwise, in step 408, the next byte to be transmitted istransferred to the transmit buffer and control passes to step 448 whichends the communications interrupt routine and causes main program 230 toresume where last interrupted.

At step 410 the received data is tested for various errors, and if anysuch errors are found, control passes to step 412. At step 412 theapparatus is set to receive and the reeive stack is cleared. Controlthen passes to step 448 described above. If no errors are found in thereceived data, control passes from step 410 to step 414 where thereceived message is tested for completeness. If the received message isnot complete, control passes to step 448 described above. Otherwisecontrol passes to step 420 in which the received message is tested todetermine whether or not it is a command to transmit data. If not,control passes to step 430 in which the received message is tested todetermine whether or not it is valid for modifying the commands and/ordata stored in IC-7. If the message is valid, then at step 432 therequested function is performed and control passes to step 412 describedabove. If at step 430 the received message is found invalid, thencontrol passes directly to step 412.

If at step 420 the received message is found to be a command to transmitdata, then control passes to step 440 in which the requested data istransferred to the transmit stack with format and addressing bytes andthe apparatus is set to transmit. Control then passes to step 406 andprocessing continues as described above.

Main program 230 is shown in greater detail in FIG. 16 and begins atstep 232. At step 234 the UPDATE DIAL FLAG variable is tested. If it isset, indicating that it is time to recompute the angular position of oneof dials 12, control passes to step 236. Otherwise control passes tostep 252. At step 236 the accumulated data from the brightest QUADSENSOR sector is tested to determine whether that data indicates thatthe associated LED 30 is either too bright (producing saturation of theQUAD SENSOR) or not bright enough. If step 236 produces a positiveresult, then the data controlling the brightness of that LED 30 isappropriately adjusted at step 238 and control passes to step 240.Otherwise control passes directly from step 236 to step 240.

At step 240 the accumulated QUAD SENSOR data is used to calculate theangular position of the dial 12 associated with that data. The algorithmused can be similar to that taught by Burrowes et al.

At step 242 it is determined whether or not the dial whose angularposition was just calculated is the most significant dial ("MSD"). Ifnot, the dial reading is stored in a temporary array in step 244 andcontrol then passes to step 250 where the dial number is incremented tobegin the accumulation of QUAD SENSOR data for the next most significantdial. If the dial is the most significant dial, then in step 246 thetemporary array and the most significant dial reading are stored in adial array, and in step 248 the dial number is preset to allow the dialreading process to begin again.

At step 252 the NEW MINUTE FLAG variable is tested to determine whethera minute has elapsed since the customer's MINAVG (MINUTE AVERAGE) demandfor servie was last calculated. If so, control passes to step 254 wherethe customer's demand over the last one minute time interval iscalculated as follows: The OLD variable (determined as described below)is subtracted from the current DISC COUNTER value to determine the REVvariable which equals the number of eddy current disc revolutions in theminute which has just elapsed (assuming that there is only onenon-reflective mark on eddy current disc 16). The REV value is dividedby an appropriate predetermined meter calibration factor to compute theMINAVG variable. The MINAVG variable is used to control the customer'sLIFELINE and DEMAND CONTROL devices, if any. Finally, the OLD variableis set equal to the current DISC COUNTER variable, the DEMAND READY flagis set to indicate that demand data is available for transmission ifdesired, and control passes to step 256.

At step 256 the PERIOD FLAG is tested, and if it is set, control passesto step 269. If the PERIOD FLAG is not set, control passes to step 258in which the just-computed MINAVG variable is compared to the customer'sLIFELINE LIMIT. If the LIFELINE LIMIT has not been exceeded, then instep 260 the data which controls the LIFELINE device (if present) iscleared to allow the customer to continue to receive service and themain program starts again with step 232. If the LIFELINE LIMIT has beenexceeded, then in step 262 the data controlling the LIFELINE device isset to cut off the customer's service and the main program starts againwith step 232. DEMAND CONTROL devices, if any, can be controlled in amanner similar to LIFELINE service.

Returning to step 252, if the NEW MINUTE FLAG is found not to be set,control passes to step 264 in which the DEMAND READY and SEND CONTROLvariables are tested. If both of these variables are set, control passesto step 266. Otherwise the main program begins again with step 232.

At step 266 the status of the PLC channel is tested and if it is foundto have been quiet for a time, control passes to step 268. Otherwise themain program begins again with step 232. At step 268 the communicationsstack is loaded with appropriate format bytes and demand data, theapparatus is switched to the transmit mode, a preamble byte istransmitted, and the DEMAND READY flag is cleared. The main program thenbegins again with step 232.

At step 269 the KWH variable is computed by dividing the DISC COUNTERvariable by an appropriate predetermined meter CALIBRATION factor. TheKWH variable is therefore the short-term demand for the DEMAND PERIODwhich has just elapsed. Control then passes to step 270 in which KWH iscompared to PK1. If KWH is greater than PK1, PK1 is set equal to KWH instep 271 and control passes to step 272. Otherwise control passesdirectly from step 270 to step 272. Steps 272 and 273 are similar tosteps 270 and 271 except that PK2 is used instead of PK1. At step 274the OLD and DISC COUNTER variables are set equal to zero. At step 276the DAY28 variable is tested to determine whether or not 28 days haveelapsed since PK2 was last reset to zero, and if so, PK2 is set equal tozero at step 278. Otherwise main program 230 begins again with step 232.

FIGS. 7-10 illustrate a particularly preferred optical system 140 fordirecting radiant energy from each of a plurality of side-by-side discs20 (e.g., five discs 20a-e) to single sensor location 50. Optical system140 is molded as a single piece of plastic material such aspolycarbonate which is preferably tinted so that it passes substantiallyonly the frequency of radiation emitted by LEDs 30. This helps reducethe effect of ambient light on the QUAD SENSOR at location 50. Opticalsystem 140 includes five circular convex lenses 142a-e, each of which isdisposed along the axis 144a-e between the associated disc 20 andlocation 50. Each lens 142 is inclined so that its optical axis iscoincident with the associated axis 144, and each lens 142 is shaped tofocus the image of the associated disc 20 at location 50.

As is best seen in FIG. 8, there are web portions 146a-f betweenadjacent lenses 142. Optical assembly 140 is bilaterally symmetricalabout the line 10--10, and also about the line 8--8. The structuralrigidity of optical assembly 140 is enhanced by integral rails 148a andb which run along each side of the assembly.

The above-described one-piece plastic lens assembly substantially lowersthe manufacturing and assembly costs of the optical portion of theapparatus of this invention.

We claim:
 1. Apparatus for reading a meter having a plurality ofrotating dials comprising:a plurality of patterned discs, each of whichis mounted for rotation with a respective one of the dials, each dischaving sectors of different radiant energy attenuating properties sothat radiant energy directed to the disc is encoded by the sectoredpattern; first means for directing radiant energy to each of the discsone at a time in succession; second means for directing the encodedradiant energy from each disc to a single sensor location; a sectoreddetector disposed at the sensor location so that each detector sectorreceives a portion of the encoded radiant energy from the second meansand produces a detector sector output signal indicative of the intensityof the received radiant energy; and third means for processing thedetector sector output signals to produce dial reading output signalsindicative of the angular position of each of the discs.
 2. Theapparatus defined in claim 1 wherein the meter is connected to anelectrical power distribution network and wherein the apparatus furthercomprises:means for applying, to the power distribution network fordistribution via that network, data signals indicative of the dialreading output signals.
 3. The apparatus defined in claim 1 wherein thefirst means comprises:a plurality of radiant energy sources, each sourcebeing adapted to direct radiant energy to a respective one of the discs;and means for energizing the radiant energy sources one at a time insuccession.
 4. The apparatus defined in claim 3 wherein each radiantenergy source is an optical radiant energy source.
 5. The apparatusdefined in claim 4 wherein the second means comprises a plurality oflenses, each lens being adapted to direct encoded radiant energy fromarespective one of the discs to the sensor location.
 6. The apparatusdefined in claim 1 wherein the third means comprises multiplexing meansfor sampling the detector sector output signals one at a time insuccession, each detector sector output signal being sampled at leastonce while the first means is directing radiant energy to each disc. 7.The apparatus defined in claim 6 wherein the first means directs radiantenergy to each of the discs intermittently, wherein the multiplexingmeans samples each detector sector output at least once while theradiant energy is on to produce a light sample and at least once whilethe radiant energy is off to produce a dark sample, and wherein thethird means further includes means for subtracting each dark sample fromthe associated light sample to produce net samples on which the dialreading output signals are based.
 8. The apparatus defined in claim 7wherein the multiplexing means takes multiple alternating light and darksamples of each detector sector output signal while the first means isintermittently directing radiant energy to each disc.
 9. The apparatusdefined in claim 1 further comprising:display means for visuallydisplaying symbolic information representative of the dial readingoutput signals.
 10. The apparatus defined in claim 9 wherein the displaymeans displays symbolic information representative of the angularpositions of the dials one at a time in a recurrent succession, andwherein the apparatus further comprises:fifth means for causing thedisplay means to display a framing indication having a predeterminedsequential relationship to the successive display of the dial angularpositions.
 11. The apparatus defined in claim 1 wherein each disc ismounted on the front of the associated dial, and wherein the firstmeans, the second means, the sectored detector, and the third means areall mounted in front of the discs to facilitate addition of saidapparatus to a pre-existing meter.
 12. The method of reading a meterhaving a plurality of rotating dials comprising the steps of:mounting apatterned disc for rotation with each of the dials, each disc havingsectors of different radiant energy attenuating properties so thatradiant energy directed to the disc is encoded by the sectored pattern;directing radiant energy to each disc one at a time in succession;directing the encoded radiant energy from each disc to a single sensorlocation; detecting the intensity of the encoded radiant energy receivedin each of a plurality of sectors of the sensor location; determiningfrom the intensities of the received encoded radiant energy sectors theangular position of the disc which was the source of received encodedradiant energy.
 13. The method defined in claim 12 wherein the meter isconnected to an electrical power distribution network and wherein themethod further comprises the steps of:applying, to the powerdistribution network for distribution via that network, data signalsindicative of the angular positions of the discs.
 14. The method definedin claim 12 wherein the intensity of the encoded radiant energy receivedin each sensor sector is detected by sampling the sensor sectors one ata time in succession, each sensor sector being sampled at least oncewhile radiant energy is being directed to each disc.
 15. The methoddefined in claim 14 wherein radiant energy is directed to each discintermittently, wherein each sensor sector is sampled at least oncewhile the radiant energy is on to produce a light sample and at leastonce while the radiant energy is off to produce a dark sample, andwherein the method further comprises the step of subtracting each darksample from the associated light sample to produce net samples on whichthe disc angular position determinations are based.
 16. The methoddefined in claim 15 wherein multiple alternating light and dark samplesof each sensor sector are taken while radiant energy is beingintermittently directed to each disc.
 17. The method defined in claim 12further comprising the step of visually displaying symbolic informationrepresentative of the angular position of each disc.
 18. The methoddefined in claim 17 wherein the angular positions of the discs arevisually displayed one at a time in a recurrent succession, and whereinthe method further comprises the step of displaying a framing indicationhaving a predetermined sequential relationship to the successive displayof the disc angular positions.